I'm very happy with my CC-121 as a single channel strip, but want to add a couple more basic faders to my setup for mixing - really, just a bank of faders for balancing levels, and then using the CC121 for getting in-depth on a track-by-track basis.
Has anyone had any luck with using another controller alongside their CC-121?

What I'm most curious about is how they interact; the CC121 follows your selected track, but what happens with the other controller? Ideally, I would hope it would also follow; I assume that the tracks would overlap (one of the channels on the controller would be assigned to the same mixer channel that the CC121 is controlling), but I can probably tolerate that. Probably.